Efforts to improve upon the performance of natural mineral oil based lubricants by the synthesis of oligomeric hydrocarbon fluids have been the subject of important research and development in the petroleum industry for at least fifty years and have led to the relatively recent market introduction of a number of superior polyalpha-olefin (PAO) synthetic lubricants, primarily based on the oligomerization of alpha-olefins or 1-alkenes. In terms of lubricant property improvement, the thrust of the industrial research effort on synthetic lubricants has been toward fluids exhibiting satisfactory viscosities over a wider range of temperatures, i.e.,improved viscosity index (VI), while also showing lubricity, thermal and oxidative stability and pour point equal to or better than mineral oil. These new synthetic lubricants may also be capable of decreasing friction and, by so doing, increasing mechanical efficiency of mechanical devices, especially where there is any significant sliding or rolling contact, for example, worm gears, other gear forms and traction drives, and do this over a wider range of operating conditions than mineral oil lubricants.
Notwithstanding their generally superior properties, PAO lubricants are often formulated with additives to enhance those properties for specific applications. The more commonly used additives include oxidation inhibitors, rust inhibitors, metal passivators, antiwear agents, extreme pressure additives, pour point depressants, detergent-dispersants, viscosity index (VI) improvers, foam inhibitors and the like, as described, for example, in Kirk-Othmer "Encyclopedia of Chemical Technology", 3rd edition, Vol. 14, pp477-526. Improvements in lubricant technology have come from new additive development addressed to deficiencies in lubricant oligomers and new base fluid development for inherently better properties.
Alkylated aromatics, particularly alkylated naphthalene, are known in the prior art as lubricant additives for their thermal and oxidative stability as disclosed in U.S. Pat. Nos. 4,211,665, 4,238,343, 4,604,491 and 4,714,7944. GB 2 078 776 discloses the preparation of alkylaromatic compounds by the reaction of olefin polymers with benzene or lower alkyl benzenes and describes their use as lubricating fluids of high viscosity, high VI and low pour point. The antiwear properties of alkylnaphthalene compounds are presented in Khimiya i Tekhnologiya Topliv i Masel, No. 8, pp. 28-29, August, 1986; these materials are thought to show promise as base stocks for lubricants.
The preparation of PAO lubricants is conventionally carried out by the catalytic oligomerization of linear alpha-olefins having between six and twenty carbon atoms employing a Lewis acid or Ziegler catalyst to form olefinic oligomers which are usually are hydrogenated to stabilize them before their formulation with additives and application as lubricants. Examples of alpha-olefin oligomerization are described in the publication by Brennan, Ind. Eng. Chem. Prod. Res. Dev. 1980, 19, 2-6. For high viscosity synthetic hydrocarbon lubricants from alpha-olefins aluminum chloride (AlCl.sub.3) is a preferred catalyst as described in U.S. Pat. Nos. 3,725,498, 3,833,678 and 4,239,927, to which reference is made for a description of the methods by which these materials may be made. These products show high viscosity index (VI) and low pour point. PAO is also prepared with promoted BF.sub.3 catalyst to produce a lower molecular weight oligomer containing residual olefinic unsaturation in the as oligomerized conditions.